Re: Uploading to Asimov

[pausch@saaf.se (Paul Schlyter)]

In article <EpTJe.8155$p%3.35450@typhoon.sonic.net>,
Andy McFadden  <fadden@fadden.com> wrote:

> The real advantage of the compressed formats, IMHO, is less about
> compression and more about having a CRC on the files.  That takes
> the guesswork out of whether or not the images are damaged.

You don't need a compression program for that!  Instead you could
use an MD5 utility, which produces MD5 hashes from the file contents.
The MD5 hashes are then put in a separate ASCII file.  This method is
used on many other web sites.

MD5 also provides better detection than CRC - not only because it has
more bits (MD5 has 128 bits, compared to 16 or 32 bits for the most
common CRC's), but because it detects not merely accidential
corruption but also deliberate modification of the files.  It is
very easy to modify a file so that it gets any CRC you want.  But
it is practically impossible to modify it so it gets the MD5 hash
you want.  I.e. with a CRC you can fairly easily modify a file
such that its CRC remains unchanged, but you cannot modify it
such that its MD5 remains unchanged.

For ensuring the integrity of the files, MD5 is much superior to CRC.

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